Enhancement is defined as any processing (other than
fashioning) which improves the appearance or durability of a gem.
Determining whether or not a gem is enhanced is part of the
previously discussed aspects of gemological investigation:

1) Species: What is this gem?

2) Origin: Is it natural or
synthetic?

3) Treatment: What enhancements, if any,
has it received?

Just to
think about: Does it matter if a gem is enhanced?

So what, if a gem
is enhanced? If enhancement makes it prettier, or more durable,
what's the big deal, and why do we even need to know? Here are some of the major issues to
consider:

Enhancement
can alter the value of a gem up or down. If it makes an unuseable piece of
gem material useable, or an ugly one pretty, then it has increased
the value of that particular piece. On the other hand, the
reality of the marketplace is that "absence of treatment"
in
itself, has
value. (Why this is so has to do both with rarity, and with a
certain philosophical value many accord to the unaltered products
of "Mother Nature".)

Take two
equally clean, natural origin rubies of exactly the same size, cut
and color: one has the color it came out of the ground with, the
other is a piece that originally was a less attractive color, but
has been color enhanced by heating. In today's market the
unenhanced stone would bring from 10 - 20% more per
carat.

**In this
case, the reasons for needing to know about a gem's treatment
status are economic and philosophical.

Although many
enhancements produce permanent changes, others are unstable and
fade, wear away, or alter with time and exposure to environmental
factors. The man-made iridescent topazes that were discussed in
the last lesson are good examples here. The coating is
microscopically thin, and care must be taken to preserve it. On
the other hand, the blue colors of irradiated and heated topazes
(like Swiss and London blue), are permanent and stable, and these
gems do not require any different level of care than naturally
colored ones.

**In this
case the reasons for needing to know about a gem's treatment state
are practical.

The general
feeling among gemologists and ethical gem merchants is that there is nothing wrong with
any type of enhancement, as long as it is fully disclosed
(including care instructions), and the gems are appropriately priced
to reflect their treatment status. Unfortunately, there are many
"ethically challenged" companies and individuals which seek to profit
by doing neither of these.

Two
Important Organizations with an Interest in Gem
Enhancement:

FTC: The Federal Trade Commission
regulates many basic aspects of marketing, advertising and commerce in
general. For gems and jewelry, the pertinent regulations regard
certain aspects of advertising and describing gems, as well as issues
of gem weights and measurements.

AGTA: The American Gem Trade
Association is an industry organization of carefully screened colored
gemstone dealers who are based in the USA. Attaining membership in
this organization involves a lengthy and rigorous vetting process
meant to assure that only dealers who ascribe to the highest
standards of ethical business practices can belong. This organization
has had extreme influence, world-wide, primarily by developing and
publicizing standards of ethical business practices for colored stone
dealers, especially as regards disclosure of enhancements.

AGTA guidelines
for gem advertising and marketing go well beyond the generalized and
generic ones found in the FTC regulations. Because more and more
countries are adopting the AGTA guidelines and their coding system,
or patterning their own after it, we will be covering portions of it
in this class.

Background:

Think of
knowledge about gem enhancement to be as a series of positions on a
continuum from 100% known to be enhanced, to 100% known to be
unenhanced:

On the one
end are gems
that we know, 100% for sure, are enhanced. This might be because the
treater has presented the material to us as enhanced, for example:
the invoice says "heat treated sapphire" or "dyed chalcedony". It
could also be because in examining the goods we find incontrovertible
evidence of enhancement. For example: microscopic examination
of a diamond reveals the characteristic tunnels made by lasers for
purposes of clarity enhancement, or testing the surface of a gemstone
bead with a swab dipped in acetone removes some of the blue dye from
it.

On the opposite
end are gems
that we know, 100% for sure, are unenhanced. This category is pretty
small actually, as unless you "dig it yourself", you are taking the
word of someone else as to the gem's treatment status. (Even in this
case, it is possible that the enhanced gem rough could have been "salted"
into the natural source!)

Not all
enhancements can be revealed by current testing methods, so in some
cases a thorough (and costly) examination by a trained professional
might only give the equivocal result of: "no evidence of enhancement
found", which is not the precisely the same thing as "unenhanced". Many
low temperature heating processes, and some forms of irradiation are
literally undetectable with today's technology. They leave no
tangible signs distinct from those which might have been the result
of natural environmental factors.

Inbetween these
extremes,
lies our degree of knowledge of the treatment status of most gems: three major stopping points on
the continuum might be labelled:

Assumed to be
enhanced

Probably/Possibly enhanced

Assumed not to
be enhanced

Gems which are
assumed to be
enhanced are
those species in which enhancement is the standard practice, or those which don't exist,
to any extent, in Nature in the treated color or form . Examples
would be blue topaz, and black onyx which are found in only tiny
quantities in Nature, but produced in huge amounts by irradiation,
and dyeing, respectively. This category would also include oiling of
emeralds, a process used on more than 90% of emeralds in
commerce.

Gems which are
probably or
possibly enhanced are those for which known treatments exist, but
range from being commonly to occasionally used. Examples would be
resin "stabilization" of turquoise, bleaching of pearls, dyeing of
jade, and heating and/or irradiation of beryls , quartzes and
tourmalines. It
is in this situation that familiarity with the detectable signs of enhancement can be
most useful. A
major goal of this lesson is to acquaint you with some of the most
important of these.

Gems which are
assumed not to
be enhanced
include those for which no treatment has yet been discovered for the
material (or at least none that is cost effective and
non-destructive). This category is highly provisional as new enhancement processes may be
developed or their safety or economics improved at any time. Examples
of gem species which currently can be assumed to be unenhanced are: spinel, iolite,
sunstone and most types of garnets.

[2 general and 12 specific AGTA codes to
be familiar with]

History
of Gem Enhancement:

The quest to make
gems look better, last longer, or sell at a higher price is nothing
new!:

As far back as
2000 BCE the Minoans applied thinly beaten gold foil to the back
of transparent stones to make them more reflective.

Pliny the
Elder (23 - 79 CE) in his famous work "Natural History" gives recipes for oiling
and dyeing gems.

An early
"consumer advocate", Camillus Leonardus, an Italian physician and
scholar, in a work called "Mirror of Stones" published in 1502 gives tips on
spotting treated gems, like using a file to test for hardness, and
hefting a gem to determine its specific gravity.

By 1932 a
gemological paper had been published listing fourteen known
heating treatments.

Just as is true
today, some of the motives of the gem treaters were honorable, and
some were not.

Major Gem Enhancements

The
surveys that follow show a few examples (there are many, many, more)
of some of the most common and economically important gem treatment
processes. In some species the treatment is used occasionally, in
others it is common, and in still others it is standard. The
organization of the species presented, within each of these treatment type surveys,
is simply alphabetical, not in order of dollar value, or frequency of
use.

Heating:
(AGTA Code = H) The most versatile and widely used treatment for gems
is heating. Depending on the gem and the desired effect, temperatures
used vary from those provided by placing the gems in direct intense
sunlight, to near melting point temperatures of 2000 degrees C;
periods of heating range from minutes to several days, and oxygen may
be present or excluded from the heating atmosphere.

The atmosphere
in which the gem is "baked" is important, as it will influence
whether its ions gain or lose electrons. That is, it will determine
if a chromophore ion will be changing from Fe3+ ---> Fe2+ or vice versa. A "reducing" atmosphere
(one without oxygen) which can either be supplied via a high tech
furnace, or simply by placing the gems to be treated in a closed
container with charcoal), causes the number to go down (+3 to +2 for
example). In an "oxidizing" atmosphere (oxygen present) the number
goes up. (**You will recall from the discussion of the causes of gem
colors in Lesson 4, the importance of the ionic state of the
chromophore.)

Heating amber: Amber is heated for three main purposes: to darken
it, to clarify it, and to deliberately add stress fracture inclusions.

When heated at low
temperatures the surface of amber gradually darkens over time. Much
of the clear amber found in nature is a light yellow to gold color,
but shades from tan to gold to orange to dark brown can be obtained
by heating. The color is usually confined to a surface layer and so
is often done after the gems have been fashioned. If desired, the
surface layer can then be partially polished or carved away to
provide contrast or create a design. (Similar low temperature heating
of ivory has been used, by unethical antique dealers, to darken its
surface and create the illusion of great age). Low temperatures must be used on these gems as due to their
organic nature, they will char, melt or burn!

In its natural
state, much amber is cloudy or milky, an effect caused by suspended
air bubbles. (If you have ever seen "whipped" honey, the appearance
is very similar). Heating such pieces in oil can clarify them to a
great extent (solid inclusions, if present, will remain however).

Finally, when
amber is heated in oil and then "quenched"(plunged quickly into a
cold liquid), characteristic stress fractures, that look like flat
disks, form. These have been euphemistically called "sun spangles",
and to some tastes, are an attractive enhancement.

The brooch photo
below shows clear and cloudy amber of a variety of colors. The
carving illustrates the surface nature of the heated color (where
some of it has been removed by the carving process), and the close up
shows the "sun spangles" in a piece of amber jewelry.

Heating
beryl: Two
species of beryl gems are commonly heat treated. Aquamarine and Morganite occur naturally
in shades of slightly greenish blue, and slightly yellowish pink, respectively, but the "market
preferred" colors are pure shades of blues and pinks. Heat is used to obtain
these preferred colors.

(The temperatures necessary to accomplish the removal
of yellow tones by changing one iron ion to another using a reducing
atmosphere, are low, and therefore, generally leave no obvious
signs.) Therefore, aqua and Morganite of pure blue or pink
color should be assumed to have been heated, unless otherwise stated.

The change is
subtle and hard to capture with a camera, especially in Morganite as
its color tone is so light, but the images below may give a general
idea of the effect.

[Unheated and heated aquamarines]

[Unheated and heated Morganites: Morganite images,
copyrighted, used with permission of
http://www.mineralminers.com]

Heating
chalcedony: Of
the many forms of chalcedony, carnelian is the only one which is
likely to be heated.

The orangey brown
color of carnelian comes from its iron oxide content, which, when
unheated, is hydrated (chemically, it has loosely attached water
molecules bound to it). This form of iron oxide is known as limonite
and is yellow to orange to brown in color. The amount of limonite
which stains the chalecdony will differ, making carnelian naturally
highly variable in tone and hue. Heat removes the bound water from
the limonite and converts it to the unhydrated form, hematite, which,
as its name suggests, is blood red in color.

Due to the low
temperatures involved (the Ancients simply put it in the sun to bake)
it is not possible to discriminate natural heating which might occur
underground during, or after, gem formation, from that which is
man-made. Therefore, if the color is significantly on the red side,
assuming it to be heated, is erring on the side of
caution.

[Carnelian briolette beads showing variation in
natural color due to variable limonite content, unheated carnelian
cabochon, a pair of very red carnelian cabs, which should be assumed
to be heated]

Heating
corundum:
Virtually all corundum gems (sapphires and rubies) have been heated.
Many different outcomes from the heating processes are possible
depending on the temperature, atmosphere, and the particular
chemistry of the material being treated.

Interestingly, in
corundum, heat: 1) can either increase or decrease color intensity,
2) it can dissolve rutile to clarify a piece, or 3) exsolve it to
create or emphasize chatoyance or asterism. 4) It can be used to
partially heal fractures improving clarity, and 5) it can diminish
the tell-tale appearance of "curved striae" in synthetics by
paritally melting these layers into each other.

We learned that
heating can remove yellow tones in aqua, but by changing the
conditions, it can emphasize them in sapphire. By using high heat and an
oxidizing atmosphere, a pale yellow sapphire can acquire a deeper,
richer color.

Blue tones in
corundum can be increased or decreased: which way it goes is controlled by
altering heating and atmospheric conditions. High temperature and
rapid cooling under reducing conditions can change the ions of iron
and titanium in pale blue sapphires to a form which results in a
stronger blue color, for example.

On the other hand,
some corundum suffers from too much blue color --> like certain
quite purplish rubies and those "midnight" sapphires, so dark they
virtually look black. Some of these gems are susceptible to
conditions (oxidizing at high temperature) which removes some of the
blue, making them much more attractive and saleable.

Corundum is also
heated to change its clarity status. This is accomplished in two
ways. Rutile is a mineral which, depending on conditions under which
the gem was formed, may be dissolved within the corundum, and
therefore not visible to the eye, or may have crystallized within the
corundum as discrete needles affecting clarity and the chatoyance
phenomenon. "Silky" corundum can be heated and cooled under precise
conditions which will cause the rutile needles to dissolve into the
corundum thereby greatly clarifying the gem; or conversely, gems with
significant dissolved rutile can be subjected to heat and temperature
regimes which encourage the dissolved rutile to "exsolve" into solid
needles.

**Check the text: On pg. 94 of the Hall text there is
a microphotograph of just the type of "silky" ruby that would benefit
from dissolving its rutile needles -- in this case they are too few
for good star potential, so dissolving them would make for a more
beautiful and valuable transparent stone.

Due to the
possibility of clarification, an increased percentage of
potentially chatoyant corundum is now sold as transparent
material, and the number of available star gems has decreased.

Gems with
significant fracturing that causes loss of transparency can be
subjected to very high heat which, by melting the thin edges of the
fractures causes partial healing and, therefore, clarification to
occur.

[A ruby
whose originally modest star potential was enhanced by controlled
heating, a pair of once silky blue sapphires, clarified by
heating]

Evidence
against heating is shown by intact silk, highly angular
included crystals, and lack of discoid fractures.

[Heated
for sure: discoid fracture in sapphire: Image courtesy of Martin
Fuller, proof of no high temperature heating: intact silk in a
sapphire]

Most corundum gems
cannot be called either way, so it is prudent to assume heating, as it is so prevalent in the
marketplace.

**Check the web: Heating sapphires is SO common that
even this company which calls itself "All Natural Sapphires" and
boldy disclaims using gem enhancements can only go so far as to claim
that "almost
all of its
sapphires are unheated". http://www.thenaturalsapphirecompany.com

Heating
diamond: After
diamonds have first been irradiated to green and blue green, they are
often heated (a process termed "annealing") to further alter their
color. Generally, such stones change to yellow or brown, but, rarely,
some pieces with slightly different chemistry or crystallography,
heat to highly desirable pink, purple or red colors.

The brown diamonds
shown below are examples of annealed stones. The second photo shows
an irradiated blue stone before and after annealing. The annealing
takes place at relatively low temperatures (well within the range of
that produced by a jeweler's torch).

Inadvertent
cases of annealing have taken place when jewelers neglected to remove
irradiated blue or green diamonds from their settings before repairs
were made --> customers were not happy to find their diamonds had
turned yellow or brown.

[Diamonds that have been irradiated then heated to
change their color, the brown stones were deliberately changed, the
yellow one was an accident]

A
New Process to be Aware of:

A new high
pressure/high temperature process for color enhancing diamonds is
beginning to impact the market. It uses the same equipment and
conditions that are have long been used to synthesize diamonds, but
the treatment time is far shorter than that used for synthesis. AGTA
(Code = HP).

Called
HPHT for short, it can produce
colorless, pink, and blue gems from some types of off-color rough or
cut stones. Due to the very high temperatures used, only
high
clarity
stones can be treated.

Not all diamonds
react to this treatment, but when they do the results are stunning
and the value of the stone jumps significantly. About 5% of diamonds
can be made colorless, and a larger percentage can be made into
"fancies". The fancy colors, are more subdued and natural-looking
than those produced by irradiation, and unlike the case with
irradiated stones, there are no obvious signs to help identify them
as enhanced, so laboratory analysis is required.

[HPHT
"Press" used by Sundance, Inc. to color treat diamonds, an example of
a "before and after" showing a dramatic improvement in color: Images
courtesy of Sundance, Inc.]

Although Sundance, Inc. is doing business honestly,
and attempting to prevent fraudulent representation of its goods, you
can see, I think, how tempted some might be to try to pass off these
relatively inexpensive enhanced gems as the higher priced "real
thing".

Heating
quartz: As with
corundum, heating quartz can have various effects. Gentle heating of
dark or muddy amethyst lightens the purple, and can reduce
unattractive grey and smokey tones. At higher temperatures amethyst
converts to yellow or orange citrine or, rarely, to yellow-green
prasiolite. (Chemical or physical factors present in amethyst mined
in only a few sites are of the sort that create prasiolite when
heated, so it is much rarer than citrine. Citrine does occur naturally, in which case Nature
has already supplied the heat, but in general, natural color stones
are notably lighter in tone than those produced with human
help.

Smokey quartz when
heated can turn yellow, also making citrine although this is less
commonly done than heating amethyst. Tiger'seye which is usually a
golden yellow color will become red upon heating.

Heating
topaz: Two types
of topaz are routinely heated. 1) White topaz, as a first step in its color enhancement, is
irradiated to brown, and it must then be heated to create a stable blue color. 2) Much natural
("precious") topaz of a yellow or orange color, some with subtle pink
overtones, is unattractively muddied with brown, which can usually be
removed or reduced by heating, a process traditionally referred to as
"pinking". As can be seen in the photo of the four stones on the
right below, the results are variable.

Both processes use
relatively low temperatures, so there is little evidence left behind.
Once again, it is prudent to assume that any blue or precious topaz
has been heated unless it can be proven otherwise. Natural blue topaz
is very
rare, and when
found it is generally quite pale, and pinking of precious topaz rough
is standard practice virtually everywhere that it is
mined.

Heating tourmaline: Heating can be useful in lightening the
color of some dark blue and green tourmalines that without such
treatment, look almost black. Unfortunately, not all dark stones
respond to the heating. In some cases, as with amethyst, muddy tones
also can be lightened or removed. For these reasons, the majority of
blue and green tourmaline rough is heated, so it is prudent to assume
it. Some red tourmalines (rubellites) can be improved in color by
heating, and though not common practice, it is occasionally done.

[Heated
blue and green tourmalines, lightened enough to be attractive, a red
tourmaline that might possibly have been heated]

As with topaz, the
temperature used for tourmaline is fairly low, so there are few
telltale heat-altered inclusions to leave evidence of it. Such
stones, however, can be more brittle than unheated ones which can
sometimes be deduced by noticing facet junctions that are abraded
more easily than the norm.

Heating
zircon:Zircon which
occurs naturally in orangey brown shades, has both a long history of
use as a gem, and a long and creative history of enhancement by
heating.

** Check the text: Page 73 of the Hall text has a
very nice picture of a step cut rectangular unheated stone that shows
the natural color very well.

The same stones
are sometimes put through a series of heat/atmospheric enhancement
regimens in an attempt to induce a change to a more desirable color
such as blue, blue-green, red, yellow, orange, or red. Individual
stones (based on their own unique chemistry) react in various ways.
The description that follows applies to the majority of zircon gems:

In the first step
of treatment, rough zircon is exposed to temperatures of around 1000
degrees C, in a reducing atmosphere where many brown stones turn
blue, some turn white and others don't change.

[1st
Round: before, brown, and after: blue or white]

Those which do not
respond may then be re-treated at slightly lower temperatures of
about 900 degrees C, in an oxidizing environment. Results can vary
from yellow to white to red.

Stones may
sometimes go through several cycles of heating, and can get rather
brittle, which may make facet edges susceptible to abrasion.

Although shades of
orange, red and yellow are occasionally found in Nature, white and blue occur
so rarely that heating must be assumed for these colors.

Heating
zoisite:When a
transparent variety of zoisite was first found in Tanzania, Africa,
there was little excitement due to its dull, brownish yellow color.
Experiments with heating, though, soon yielded gems of a beautiful
blue-violet color. As it turns out, heating was turning one of the
color axes of this naturally trichroic gem from yellow-green to
colorless, and allowing the less dominant blue and violet colors to
be clearly seen. "Tanzanite" was born. As is so commonly true of gem
rough, some individual pieces have atypical chemistry or
crystallography, and react differently to treatment than most. In the
case of this type of zoisite a very small percentage of the gems heat
to an attractive green to blue green color. Dubbed "Green Tanzanite"
(a misnomer, but one that stuck), such specimens have high value as
collector stones, and are quite beautiful in their own
right.

There are two major groups of gems that aren't
heated: 1) heat sensitive gems like opal, apatite, pearls, and
turquoise, and 2) those for which heating makes no improvement, or
isn't economical such as garnet, spinel, chrysoberyl, iolite,
peridot, sunstone, moonstone, jade, and most collector stones. If
unheated is what you want, that is fine, but outside of the groups
listed, you can expect to pay a premium for unheated goods, and some
types of gems like blue zircon and Tanzanite will be off limits
entirely.

Another point
to keep in mind is that "unheated" doesn't mean the same thing as
"unenhanced",
although there are those who can profit from implying it does!

I have seen
several dealers on independent websites, online auctions, and at gem
shows that proudly advertise their wares as "unheated" when their
goods have been, dyed, coated, irradiated, oiled or in some other way
enhanced. Naive buyers can be deluded into thinking they've purchased
an unenhanced stone.

Irradiation:
( AGTA Code = R)
After heating, the most commonly used treatment for gem enhancement
is irradiation. With some important exceptions (like diamonds),
treated stones are usually not distinguishable from untreated ones, as gems are
often subject to similar, but natural, irradiaton effects during, and
after, their formation.

A variety of
sources of, and processes for, irradiation have been tried, some,
proving unsatisfactory, have been abandoned, others are still in use.
The earliest experiments with irradiating gems used alpha particles
(helium nucleii) which worked as desired, but left the gems with
strong and highly persistent residual radiation. Today, beta
particles (electrons) generated in linear accelerators, neutrons from
nuclear reactors, and gamma rays usually from radioactive cobalt
sources are used.

Although the
bombardment with neutrons and, to a greater extent, with electrons,
can leave some residual radioactivity, its duration is relatively
short. Government agencies in the USA, and other gem irradiating
nations, have strict regulations for the holding and testing of
irradiated gems to assure that they are not released to the public
until they are safe to handle and wear.

As we saw to be
the case with heating, different types and durations of irradiation
produce different results. Combining this fact with the idea of
individual variation in gem chemistry, and that irradiation may or
may not be followed by some sort of heating process, and we can begin
to appreciate the tremendous diversity of possible
results.

Irradiating beryl: Colorless beryl (variety = Goshenite) can be
irradiated to stable shades of yellow to gold (variety = golden beryl
or heliodor). Unenhanced golden beryl is also common, and it is
essentially impossible, outside of a large gemological laboratory, to
tell whether it was man or Nature that supplied the color producing
irradiation.

[Goshenite, golden beryl]

A
boondoggle perpetrated on the gem buying public several decades ago,
is still remembered by some wary dealers and buyers. Some beryls,
with an unusual chemistry, turned a vivid and attractive blue when
irradiated. They were rushed into the market with much fanfare under
the tradename "Maxixe" beryls. The fly in the ointment was that these
stones were unstable in light, and reverted to their intially colorless
state relatively quickly under normal use conditions.

There would be
little point in bringing up this unsavory memory, except that in 2003
explorers in Canada unearthed a bright blue deposit of beryl
reminiscent of the Maxixe color. This material is colored by iron
(not irradiation), and the color is stable. As of yet, the mining
efforts have not yielded any facet quality rough, but exploration is
proceeding. The only known deposit is presently owned by "True North
Gems" and their material, already popular with collectors, has been
christened "True-Blue Beryl".

Irradiating
diamonds: As
presented in the section on heating gems, diamonds irradiate to green
or blue green. Another color which is commonly produced via
irradiation is "black". Well, actually, it is not black but a very,
very, dark green, and the visual impression is definitely black.

Diamonds do occur
naturally in black (if they are highly included), but irradiated
"black" diamonds, when subjected to very concentrated light source,
like a fiber optic light, show green color at the extreme edges where
the girdle or facets are thinnest, whereas this is not true of
unenhanced black diamonds. Virtually all the black diamonds used in
jewerly today are the irradiated type.

You will recall
that these irradiated stones can then be annealed (heated) to brown,
yellow or, less often, some of the rarer fancy colors like red. These
heated and/or irradiated colored diamonds tend to have more vivid
(some might even say "garish") colors than naturally colored fancies.

Unlike what is
seen with the majority of species which are irradiated, the process
does tend to leave tell-tale signs in most diamonds.
Patterns of color zoning that show up microscopically, with certain
lighting conditions, can usually give the trained observer evidence of the treatment.

With enhanced blue
colored diamonds, though, there is a definitive test--> electroconductivity.
Diamonds that come by their blue color naturally contain boron impurities which allow them to conduct
electricity, irradiated blues get their color by the effect of
irradiation on their crystal structure, and like all other diamonds,
don't conduct.

Irradiating
pearls: One of
the many possible enhancement processes that are used to change color
in cultured pearls, the use of gamma irradiation has different
effects on fresh and saltwater cultured pearls.

When saltwater
pearls, like Akoyas, are irradiated, it turns the bead nucleus (made
of shell) dark, which then shows through the unaffected translucent
nacre layer making the pearl look grey or perhaps grey-blue. In the
case of cultured freshwater pearls, the irradiation actually affects
the nacre layers creating silver, gold, black and even multi-hued,
often intensely metallic looking colors. (This difference is due to
the slightly different trace element chemistry of nacre produced in
fresh vs saltwater.)

The treatment in
both cases is stable. With saltwater pearls it is usually possible to
get a magnified view down a drill hole which will reveal the darkened
bead nucleus. Identifying irradiated freshwater cultured pearls
(which usually have no bead nucleus) can be as simple as becoming
familiar with the natural color range of these gems. Once that is
accomplished, the completely unnatural looking irradiated stones jump
out at you and identify themselves!

**Check the web: This GIA report was done shortly
after the 9-11 incident. At the time, some letters and parcels were
being irradiated by the US Postal Service as a counter bio-terrorism
measure. The before and after pictures show how sensitive pearls are,
even to low levels of radiation: http://www.gia.edu/newsroom/608/384/news_release_details.cfm

Irradiating
quartz: Colorless
quartz, rock crystal, is irradiated to produce smokey quartz in
shades from light to very dark brown or grey-brown. The smokey quartz
found before modern irradiation techniques were developed, and a
proportion of that mined and sold today, comes pre-irradiated by
Mother Nature.

A relatively
recent discovery of a unique type of rock crystal at a particular
series of mines in Brazil gives quite different results when
irradiated. The resulting material known variously as "neon" "lemon"
and "oro verde" quartz has a highly saturated, slightly greenish
yellow color. Due to its striking color and its availability in
inexpensive, large, clean pieces, it has become the recent darling of
carvers, concave facetors and fantasy cutters, as well as a staple of
the home shopping channels, and internet gem auctions.

Once again, with
smokey quartz, we have a case where it is difficult to impossible to
determine the origin of its color, and it is best to assume it has
been irradiated by man, in the absence of proof to the contrary. Not
so, with the yellow material, as its only known source is from the irradiator's
factory.

Irradiating
scapolite and spodumene: Although these two gem species are likely to be
unfamiliar outside of gem circles, they provide some interesting
examples of the effects of irradiation. Scapolite is found naturally
in light to medium shades of yellow, and also in pale lavender. The
yellow material can be irradiated to a much deeper, and more
brownish, shade of lavender than that which occurs naturally.

Spodumene occurs
naturally in colorless, light to medium pink/lavender (Kunzite), and
very
rarely in a
chromium colored, grass to emerald green stable variety known as
Hiddenite. Kunzite can be irradiated to a light to medium green color
which is often given the misnomer of Hiddenite, and sold for inflated prices to naive
collectors. Not only is the irradiated material not Hiddenite, as its color does not come
from chromium, but it fades quite noticeably in the light, a fact too
rarely included in the sales pitch.

Irradiating
tourmaline:The world's
supply of attractively colored pink to red tourmaline has recently
been greatly increased by new discoveries. Some Brazilian
tourmalines, formerly rejected due to poor color, and the majority of
the large new deposits being found in Africa, are irradiated to
diminish brownish tones. The permanent improvement in appearance
(alas, not all pieces are susceptible) is similar to that displayed
in the two stones below:

[Typical "before and after" colors of some low grade
tourmaline that is susceptible to drastic improvement in color after
irradiation ]

Irradiating
topaz: In terms
of sheer carat weight, and probably also in terms of economic value,
blue topaz is the most important irradiated gem. Colorless topaz is
plentiful and inexpensive, but not all of it will irradiate
successfully. Treaters generally screen the rough with an inexpensive
gamma ray treatment which identifies the rough which will benefit
from further irradiation, before proceeding with more costly and time
consuming treatments.

These "good
candidates" then go to either a linear accelerator to be bombarded
with electrons, or to a nuclear reactor to be exposed to neutrons.
Depending on the duration and type of irradiation, and the sort of
heating process used afterward, the results vary from sky, to Swiss
to London blue. Other slight color variations have been produced and
given their own tradenames like "electric blue" and "neon blue".

London blue is the
scarcest and most expensive type because it requires neutron exposure
(most expensive process), and the longest holding times. Now that so
many other types of gem materials are being irradiated, topaz
treaters are having to pay more to "book" accelerator or reactor
time, and prices for these once quiet inexpensive gems have
correspondingly risen.

With most gem
materials, much, if not most, of the cost of the finished gem, is
associated with the gem rough itself. Blue topaz is an interesting
exception to this, as the rough is the least expensive part, with fashioning, and
even more so, treatment, responsible for the bulk of the
costs.

The irradiated
colors are stable, and the gems are perfectly safe to wear, but the
dual heat/irradiation processing does leave them somewhat more
brittle than unirradiated stones. Added to the natural tendency for
cleavage, this makes blue topaz one of those gems which, despite its
hardness of 8, is not a good choice for daily wear rings or
bracelets.

The introduction of huge amounts of blue topaz into
the market place in the last several decades has had some interesting
side effects on other gemstones.

1) For a time,
it depressed the prices of aquamarine, as sky blue topaz made a
pretty good aqua simulant at about 1/10th the price. With time,
though, most aquamarine lovers went back to their original gem
choice, with the ironic twist of a noticeable decrease in the
traditional preference for heated "pure blue" stones. More and more
aqua fanciers are now seeking out the greenish blue unheated
stones--> possibly because these are less likely to be mistaken
for the ubiquitous and inexpensive blue topaz!

2) The other
effect has been to literally wipe out the identification of the word topaz with the color
yellow. Yellow, or precious topaz, was, until the advent of
irradiated blue, the most common and familiar type, and is still the
traditional birthstone for the month of November.

[For
centuries, these were the colors that the word
"topaz"evoked!]

Food for thought:
(Answers to
the questions are found at the end of the lesson)

Question 1:
Your friend wants an untreated gemstone and has found a dealer with
some beautiful golden beryls. The dealer assures him that they have
not been heated. He asks for your advice. What do you tell
him?

Waxing:(AGTA Code = W) When the surface of a gem is coated
with colorless wax, (or oil) the process is termed waxing. Generally,
this treatment is used with stones with a vulnerable, porous surface,
or those with microscopic surface imperfections whose polish luster
can be boosted with it. Porous materials like turquoise that have
been waxed, are thereby, at least partially, protected from absorbing
skin oils and other environmental contaminants.

Although, not
permanent, the gem community tends to adopt an extremely forgiving
attitude toward this treatment, as it is both a very long standing
tradition, and a simple matter to re-wax the gem. (Paraffin and
beeswax are the traditional materials used, and re-doing a gem can be
as simple as painting on melted wax and buffing off the excess).

Most of the
world's highest grades of turquoise and jadeite can be assumed to
have been given this treatment. It is also occasionally used with
lapis lazuli, rhodocrosite, serpentine, variscite and
Amazonite.

Dyeing: (AGTA Code = D) Dyeing is relatively easily
accomplished with porous gems and those crystalline gems which are
aggregates. The pores and the spaces between the microcrystals allow
the dye to be taken up. Single crystal gems, however, are
not good candidates for dyeing as they will only take up
dye where they have surface reaching fractures.

There is really
only one
case in
which dyeing is an "accepted industry standard", and has no effect on
the value of the gem: black onyx. All other instances of dyeing (when
disclosed) negatively affect the value of the gem, in some cases,
dramatically.

Examples of porous
and aggregate gems which are frequently dyed are chalcedony, jade,
coral, pearls, and howlite.

There are some
cases where the absorption spectrum of a gem can identify specimens
which are dyed, but they are rare. The usual ways of detecting dyed
gems are:

2) Testing with a
solvent, a destructive test, yes, but one which can usually be done
in an inconspicuous area. Useful solvents are acetone and denatured
alcohol, but not all dyes are soluble in them, so a negative test in
not conclusive.

3) Comparison to
the normal range of gem colors and evaluation of the avialability and
cost --> naturally colored chalcedony in unknown in hot pink for
example, and Nature doesn't yield neon green pearls. Saturated,
medium dark, lavender natural color jade is worth a King's ransom, so
pieces of that color seen on ebay for $10 are very likely to be dyed.
(Compare the
color of the inexpensive jade beads below with the picture of the
very expensive natural color lavender jade ring
above).

One of the most
commonly dyed materials in today's marketplace is howlite, an
inexpensive, porous, white mineral that generally has grey to black
veining. It has been used to simulate turquoise, lapis, rhodonite,
and other opaque gems. The dye penetrates only a short distance into
the gem, so scratches and chips are revealing, but when undisturbed,
a piece can be quite convincing.

When single
crystal gems are dyed, they must be fractured first. In order to
achieve this, the age old method is "quench crackling". Generally
this is done by heating the gem, and plunging it in cold water, but
strong ultrasonic vibrations have been used to accomplish the same
thing. Dye can then be absorbed into the fractures which, when
numerous enough, give the piece an overall color.

[Two
pieces of quench crackled, dyed rock crystal quartz, the pink one has
been magnified and shows clearly that the dye is only in the
fractures]

In the great
majority of cases, the dye is a chemical or pigment of either natural
or synthetic origin. An example is the use of silver nitrate, a
chemical that darkens on exposure to light, which has been used on
pearls for many years.

There are a couple
interesting cases, however, which involve "carbonization". Chief
among these is the production of "black onyx". Here's one of those
cases where a misnomer continues in use, just because of familiarity
and convenience. (Onyx by definition is has color bands, so a solid
black material just doesn't qualify). There are very small amounts of
black chalcedony found in Nature, but the virtually all of that in
commerce is carbonized chalcedony.

Colorless to light
grey chalcedony is soaked in a sugar solution until its internal
pores are filled with it, then it is boiled in sulfuric acid which
"carbonizes" the sugar turning it black. There are now microscopic
sized black specks throughout the piece, giving it a uniform and
stable black color. When I was first learning about gems, I just
couldn't believe that this primitive method, developed hundreds of
years ago, was still the major mode of production...but it is!

A similar process
is used to color certain matrix opals (particularly those from
Australia's Andamooka region), whose matrix is a light color, giving
little contrast to the patches of color of the opal within the
matrix. The result of the darkening of the matrix is an improvement
in contrast and therefore in the appearance of the color
play.

Bleaching: (AGTA Code = B) Probably the most routinely bleached
gem, is pearl. Historically, long before cultured pearls were
invented in the early 20th century, pearl fisherman would spread
their treasures out in the bright sunshine, carefully rotating them
over a period of time, which tended to lighten and even the color,
and diminish some unsightly dark spots. Light is still used in some
pearl processing facilities. (Anyone whose hair gets lighter in with
long exposure to sunshine, or whose window drapes have faded over
time, will realize how effective a bleach light can be.

Besides its use in
removing blemishes and evening out color, bleaching is a tremendous
aid to manufacturers in matching pearl colors. Today's pearl consumer
demands that each and every pearl in a strand, is exactly the same
shade---> Mother Nature prefers to make a wide variety of shades,
even within the same species of oyster or mussel, living in the same
body of water.

In addition to
light, chemicals such as hydrogen peroxide (Lady Clairol, anyone?)
and chlorine (as in Clorox bleach), speed up the process, but on
delicate organic gems like pearl and coral, must be used at low
strength and with care.

Golden coral is
rare and valuable, so is black coral. Depending on the ups and downs
of the market, the vagaries of supply, and prevailing public tastes,
there are times when black coral is bleached to gold (peroxide is
used).

[Bleached black coral beads: Image courtesy of
www.stonesnsilver.com]

Jade is another
frequently "bleached" gem, but in this case strong acids are used
which really
aren't bleaching the color to a lighter shade, they are literally
dissolving away discoloring inclusions. Such bleached jade requires
further treatment to seal the cavities formed by bleaching. (See
below.)

Acid bleaching is
also used in conjunction with laser drilling in diamonds to remove
"carbon" spots and other discolorations. The laser creates a narrow
channel by which the acid can penetrate the interior of the diamond
and do its work. As with jade, this process is generally followed by
one which "fills" the cavity. (Again, see below)

Impregnation (aka
"stabilization"): (AGTA Code =
I)

When a colorless,
hardened, resin is suffused throughout a porous stone to make it more durable
or improve its appearance, it has been impregnated. A common market
term for such gems is "stabilized". There is only one imporant type
of gem for which this treatment is essential--> without impregnation, ammolite is
too fragile to withstand fashioning or wear. Unenhanced specimens,
exist, but are suitable only for display.

Other gems like
jade or turquoise are commonly treated in this manner. Low grades of
highly porous turquoise that may have nice color, but are excessively
fragile, or near impossible to polish, can be greatly improved by
resin impregnation. "B" and "C" jades, after being acid bleached have
resin infused into the resulting cavities (if the resin is colored,
then the piece is considered dyed, "C" jade).

[Impregnated gems: ammolite pair, turquoise cabochon,
"B" jade ring]

Oiling:
(AGTA Code = O)
and
Filling: (AGTA
Code = F) Both of these
types of treatments involve the filling of surface reaching fractures
or cavities with colorless oils, resins, or glass. They are done for the same
reason: to clarify a gem, by decreasing the relief of the fracture or cavity. The
difference between them hinges on whether the filling material is
essentially a liquid (oil or unhardened resin) or solid (hardened
resin or glass).

Of the two, oiled
gems are more accepted in the gem marketplace and do not depress value greatly. Even
though the oil treatment is temporary, the favorable viewpoint comes
both from the long standing and widespread use of gem oils, and the
fact that it can be successfully be re-done if necessary. Virtually
all emeralds are oiled, some as rough at the mine site, others only
after they are cut. Certified unoiled emeralds bring a 10% - 20%
price premium. If the oil is colored, then the emerald is considered
to be dyed, and its price is much more severely affected.

[Emeralds: routinely oiled to improve
clarity]

Filled gems are
another matter. Although it can be argued that the filling, being
hardened, is less likely to evaporate or be dislodged by cleaning and
wear, several factors create a generally negative impression that
translates to a drastic effect on gem prices.

The solid resins
can discolor and become more opaque with age, and since they cannot
be removed, will then permanently degrade the gem's appearance.
Fairly large areas can be filled with solids, which are less durable
than the host gem and can become scratched, chipped or dulled with
wear. This process is primarily used with rubies and diamonds, both
very valuable gems, so it must not be forgotten that these chunks of
glass or plastic resin are adding weight to the gem. That is, adding
weight of a material which is not valuable, but which the customer is paying
for.

Until just
recently, diamonds were the only major gem for which glass filling
was a concern. Now, however, the number of glass filled rubies in the
marketplace has risen to the point where gem professionals and alert
buyers need be wary. Glass or plastic filled gems are worth only a
small fraction of the value of their unenhanced equivalents.

Fortunately, there
are several ways to detect glass or plastic areas in gems. Under
reflected light, the luster difference between a ruby or diamond, and
its glass filler are easy for the trained observer to spot. Some
fillers fluoresce and give themselves away. For those which are
confined to thin fractures, the "flash effect" is a tell-tale sign.

The
Flash Effect:

As a
gem is rocked and tilted under appropriate lighting and
magnification, these thin filled areas will first flash one solid
color like orange and then, at a different angle, a different color
like purple. Novices may confuse this with the cleavage rainbow seen
in unfilled fractures, but in the flash effect, only one color is
seen at a time.

Gems which are
properly disclosed as oiled or filled, should include appropriate
care instructions. For example, oiled emeralds should not be steam or
ultrasonically cleaned. Jewelry containing filled rubies and diamonds
should not be repaired or resized without removing the gems from the
settings, as heat from a torch or immersion in metal cleaning
solutions can cause melting or etching of the filler.

Food for
thought:

Question 2: You
walk into a jewelry store with your brand new gift ruby ring, and the
emerald brooch you inherited from Aunt Minnie. You want the ring
sized, and a new closure soldered onto the brooch. You ask the
jeweler for the estimated charges including dismounting and
remounting the gems. She says dismounting will not be necessary. What
should you do?

Laser
drilling: (AGTA
Code = L) Thus far, this treatment, a type of clarity enhancement,
has been seen only in diamonds, and is virtually always combined with
acid "bleaching" and fracture filling. The purpose of the tunnel
created by the laser is to provide a channel for the acid and glass,
or resin, to enter. The entry points are tiny, as seen in first photo
(red arrows) and can be easily overlooked, but microscopic
examination (usually 10x is sufficient) makes this treatment one that
can be positively identified.

Diffusion:
(AGTA Code = U)
When gems are diffused, they are heated to very high temperatures,
just to the verge of their melting points. This heating is done in
the presence of a material which contains chromophores such as
titanium, chromium or other atoms, which are then able to diffuse
into the stone's surface or interior to change color or create
phenomena. Two such processes are currently in use: 1) surface
diffusion, and 2) bulk or "lattice" diffusion.

Surface diffusion has been around for decades and, until recently, was
pretty much confined to use on blue sapphires and the occasional
ruby. By packing already faceted, light colored stones into a
container with powdered titanium and iron, and heating to very high
temperatures, a thin surface layer rich in these chromophore elements
is formed, which through selective absorption, greatly darkened the
apparent blue color.

Such stones must
always be repolished afterward as the high heat tends to mar the
surface. In the repolishing process it is inevitable that some of the
thin layer is unevenly removed, so that when viewed under immersion
and/or in diffused light, an uneven pattern of color--> paler on
some facets than others and darkest at the edges of the facets, can
be seen.

If the diffused
stone has inclusions at all, these will also show the typical signs
of high heat, such as partially resorption of silk, partial melting
of crystals, or stress fractures. With such obvious signs of
treatment, only the unschooled or unwary buyer is likely to be duped.

Below is a picture
of a 1.53 ct. sapphire. A beautiful stone: top color, eyeclean, and
reasonably well cut. In today's market one might expect to pay
between $1000 and $1500 per carat, retail, or even more in an upscale jewelry store
for a sapphire with this kind of appearance. This stone's actual
retail price was $150 for the piece, or less than $100 per carat.
What a bargain, you say --> and why so cheap? (No, it is
not a synthetic!)

[An
attractive, color enhanced, natural sapphire]

The price paid,
was, however, appropriate to the stone. It is a natural origin sapphire, but it is has
been color enhanced by surface diffusion. The lovely color layer has
a thickness of much less than one millimeter, the rest of the stone
is either colorless or an unappealing pale blue or grey.

Such stones
represent a bargain, as long as the customer understands the
limitations inherent to them. Any scratch, chip or nick will remove
the color layer revealing a light spot, and the stone cannot be recut
or it would lose its color entirely. As a stone to be used in a
pendant or earrings or even a ring worn once in a while, it will look
beautiful for many years, but it is not an appropriate choice for a frequently worn ring or
bracelet.

You can see from
the photo, that looking at the stone in ordinary light doesn't tell
you the source of its color. Below are two 10x magnified photos of
this same gem, (you can do this kind of observation with your loupe,
no fancy microscope is necessary).

In the first, the
gem is seen in diffused light, in the second, it is immersed in water
and viewed with diffused light. Both photos give unequivocal evidence
of surface diffusion. Look closely and note the color differences
from facet to facet (natural color zoning does not follow facet shapes), especially
telling is the way the color is darker along the keel and at many of
the facet boundaries.

[Magnified views of a surface diffused blue sapphire:
under diffused light, under immersion in water with diffused
light]

Making Stars

When titanium
dioxide (rutile) is surface diffused into a sapphire, and the heating
and cooling is controlled so that it exsolves into needles, asterism
is created in the stone. Again, you are looking, in the photo below,
at a natural sapphire, but one that has been surface diffused
with rutile. Such gems are very inexpensive compared to unenhanced,
natural star sapphires. In comparison to an unenhanced star stone,
the star figure is stronger, more even, and seems less mobile as the
light source shifts direction.

[A
surface diffused star sapphire]

A recent entry
into the world of surface diffused gems is topaz, now available in
bright colors such as green and red as well as bi-colors. The
advertisement below is from an ethical company (RioGrande), which is
one of the major suppliers of gems to jewelers: notice the
enhancement code (U) and the appropriate warning about
recutting.

[Graphic courtesy of RioGrande Corp.]

In
2004 Leslie and Company introduced the first surface diffused
bi-colored topazes to complement their existing line of tradenamed
diffused topaz gems.

[Surface diffused topazes: Images courtesy of Leslie
and Company]

Bulk or lattice diffusion was discovered to be occuring in 2003
when stones that began appearing the market in 2002 were critically
examined. The gems were sapphires of an extremely rare and valuable
color called "padparashah" (orangey pink). The inexplicably large
numbers of fine colored stones suddenly available, raised questions
that led to a fervor of activity among the staff gemologists in
organizations such as AGTA and GIA.

Athough the
treaters were freely acknowledging that the gems had been heated,
they insisted that that was the end of the story. Adding to the
confusion, the stones did not fit the profile of diffused gems as the
color penetrated well into the interior--> in many causes
completely throughout the stone.

Suffice it to say
that they were finally demonstrated to be the result of a
new diffusion process using the
light element beryllium (Atomic number = 4) as colorant. With its
small atoms, the beryllium chromophore was able to diffuse much
further into the heated stones than titanium or chromium with their
much larger atoms. The source stones were primarily light pink
African sapphires which were then being were treated in Thailand.

[Bulk
diffused "padparashah" sapphires]

The "pre-discovery" prices were extremely reasonable for naturally
colored, or simple heat treated paparashahs, but outrageously
inflated for diffused goods. In the interim between the time the
stones were stealthily introduced into the market, and the time their
true nature was understood, quite a few greedy collectors and dealers
re-learned the old lesson "If it seems too good to be true, it
probably is".

Viewed under
diffused light and /or immersion, most of these gems show normal
color patterns. Although they do have inclusions typical of high heat,
positive
identification of a particular gem as being beryllium diffused,
requires the services of a large gemological laboratory.

Although they are
considerably more durable than surface diffused stones, recutting
could still be a risky proposition, especially on larger stones.

Coating: (AGTA Code = C) Coated gems are those that have been
treated with surface enhancements such as laquering, inking,
painting, foiling, or sputtering of a film to enhance color, improve
appearance or add phenomena.

Coating has a long
history: from use of gold foils in antiquity, to the painted back
Rhinestones of the 19th century, to today's iridescent metallic
coatings. Coatings are usually fairly easy to detect, but can escape
notice if they are applied only to back of the gem (as in a
"foilback") and the gem's setting is fully closed. The coatings of
foilbacks range from crude and obvious, to sophisticated and well
hidden, as seen below.

Perhaps the most
nefarious of the fraudulent uses of coating is an old (but still in
use) trick of putting a tiny drop of indelible blue ink or paint
underneath the prongs holding an off-color diamond in its setting.
The prong hides this dot of color from all but the most experienced
eyes. The effect of the light reflecting off those blue areas and
mixing with the generally yellowish light emerging from the gem,
makes the yellowish stone appear shades whiter. (As an example, this technique
might raise a stone's apparent color grade from M to F allowing the
seller to make an undeserved profit.)

The most common
coatings in today's gem market are the metallic vapor films that
create iridescent gems.

There are no
overall rules, as some enhancements increase durability, while others
decrease it. But these general precautions will protect almost any
enhanced gem: avoidance of solvents, ultrasonic and steam cleaning,
gentle wear, protective settings, avoidance of recutting, and removal
of gems from their settings prior to jewelry repair.

Answers to the thought exercises for this lesson. (If
you don't understand something in these answers it's time to email me
and ask!)

1): You might make
sure that your friend understands the difference between "unheated"
and "unenhanced." Most likely he is under the impression that they
mean the same thing. Few people who have not studied gems realize the
vast number of treatment possibilities there are. You could also
mention that a lot of the golden beryl in the market has been
irradiated. A possible suggestion would be that he ask the dealer,
point blank, whether the gem has had any enhancement at all. (On the other hand
you might like to just keep your mouth shut, and smile, and agree
that they are lovely).

2): The safest
thing to do would be to walk right out and find another jeweler. The
new ruby ring could be glass filled, the emeralds are almost
certainly
oiled--> in either case the heat from the jeweler's torch (even
when methods are used to keep the gems isolated from the heat) can do
major damage. Even if the gems were completely unenhanced, there is
still the possibility of damage from inclusions due to thermal
expansion.

You have now
completed the web lecture for the eighth lesson!

Go
back the the course website to: 1) complete and submit the homework
assignment on the text readings and assigned web essays 2) take the
non-graded practice quiz on this web lecture 3) post a comment to the
discussion board for this lesson, and 4) when it is available, complete the graded quiz
based on this web lecture.

When
you're ready, proceed on to Lesson Nine: Synthetics and
Simulants